ASoC: rt5640: Add function for enabling DMIC from ACPI probed machine

There is no code enabling DMIC clock in systems that don't provide platform
data for rt5640 after commit 71d97a79 ("ASoC: rt5640: Use the platform
data for DMIC settings").

I think it's worth to keep this static DMIC clock and alternative data pin
setting during probe time. For making possible to use DMIC from ACPI probed
machine (prior ACPI 5.1 with _DSD) this patch moves DMIC configuration to
new exported rt5640_dmic_enable() that machine drivers can call.

Please note, this patch moves DMIC configuration from i2c probe to codec
probe in case platform data for rt5640 is set.

Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Cc: Oder Chiou <oder_chiou@realtek.com>
Signed-off-by: Mark Brown <broonie@kernel.org>